> I just purchased a fluval FX5 filter and was wondering what filter media would be best for my set up. I have a 40 gallon tank with three Goldfish. Two are almost 7 inches in size The other is a Fancy tailed Big Bellied about 4 inches nose to tail. Also is a 3 inch catfish and a 4 inch Pleco. My tank is always dirty so we got the FX5 thinking it will help.
I have an FX5 on my 220 gallon, and it works well with the sponge media
it comes with, along with carbon and PolyFilter. However, I believe a 40
gallon tank is going to be too small for the fish you have. I would
suggest upgrading to at least a 75 gallon (48" x 18").